Investigations are proposed to determine the effect of a teratogen on the biochemical maturation of the liver. The activity of enzymes participating in important functions of the liver will be analyzed in the normal and teratogen-treated rat during the transition from prenatal to postnatal existence. Three functions will be studied: (1) maintenance of blood glucose, (2) metabolism of lipids, and (3) the excretion of bilirubin and nitrogenous wastes. A teratogenic dose or a subteratogenic dose of aminothiadiazole (a known teratogen) will be injected into rats either at day 9, 13, or 17 or pregnancy, enabling three different periods of prenatal development to be studied. Fetuses will be recovered at day 20 for study of enzymes from the late fetal cluster. Newborn animals will be taken one day after birth for study of enzymes from the late suckling cluster. Samples of maternal liver will be analyzed at the same time.